The present invention relates to a method of mixing a raw material composition used in the preparation of materials which may ignite or explode, such as igniters, and, more particularly, to a method of mixing a raw material composition for igniters, etc. which enables the mixing of the raw material composition to be conducted in a safe manner with high homogeneity.
Great care should be taken in handling igniters, etc. because they evolve a large amount of a high-temperature gas due to a rapid redox reaction. The igniters, etc. have hitherto been prepared by homogeneously mixing a raw material composition comprising a finely divided metal powder or a reducing salt, such as azide, and a metal oxide, such as copper oxide or lead oxide, or an oxidizing salt, such as a salt of nitric acid or a salt of perchloric acid; and molding the resultant mixture by pressure molding etc. into a pellet having a suitable shape.
It is known that an excessively large particle diameter of the raw material composition and insufficient mixing in the above-described step of mixing hinder the progress of an intended redox reaction during the use of the product, which brings about variation in combustivility, particularly variation in the burning velocity of the pellet, so that it becomes difficult to evolve a high-temperature and high-pressure gas in a predetermined time. For this reason, in a generally adopted method, individual raw material ingredients are ground into fine particles of the order of a few microns or less and then sufficiently mixed.
However, once such a mixture comprising fine particles is ignited, it brings about such violent burning or deflagration that handling thereof involves great danger. This makes it necessary to limit the amount of each ingredient to be mixed in one run to a small amount , which has led to a problem of low productivity. Further, remote control of the operation through a blast wall is necessary for the purpose of securing safety, which necessitates unfavorable expenses for facilities therefor.
Meanwhile, a known, safer mixing method in preparing the above-described raw material composition comprises adding a low-boiling point liquid, such as methanol or ethanol, which does not dissolve any of the ingredients, mixing the ingredients, and removing the liquid by heating or the like. However, this method has a drawback that the process becomes very complicated.
In a rapid dehydration and crystallization method proposed by the present inventor in Japanese Pat. Laid-Open No. 1077/1978 in connection with a gas generating agent comprising two or more water-soluble salts, such as niter and sodium azide, wherein water-soluble organic solvents, such as methanol, ethanol or acetone, are used . An aqueous solution of two or more salts in a high concentration at 50.degree. to 60.degree. C. or above are poured with sufficient stirring, into a water-soluble organic solvent, such as methanol, ethanol, isopropanol or acetone, of an amount at least 20 to 30 times as large as the aqueous solution is cooled to about 0.degree. C. or below. It is necessary to provide a step of collecting precipitates by filtration and drying and a step of recovering the solvent by distillation, etc., which renders the procedures so complicated that this method is economically impractical